Does the phylogeny of pelomedusoid turtles reflect vicariance due to continental drift?
The turtle hyperfamily Pelomedusoides has been long regarded as one of the best reptilian examples of the shared biological history of Africa and South America, and of vicariance due to continental drift. The currently accepted phylogeny of the Pelomedusoides is based on morphological and serological evidence. This study uses molecular data to examine the relationships within the Pelomedusoides and tests the hypothesis that the speciation within this group was caused by the separation of the Gondwanan continents. Methods
Phylogenetic analysis of 921 bp of 12S and 16S mitochondrial rRNA obtained from GenBank. Results
Our analysis resulted in a well-supported phylogenetic hypothesis for the extant Pelomedusoides that does not agree with previous hypotheses based on morphology and serology. The new hypothesis of pelomedusoid relationships is (Pelusios + Pelomedusa) (Peltocephalus[Erymnochelys + Podocnemis]). The molecular evidence supports the monophyly of the Podocnemidae and Pelomedusidae of de Broin (1988). However, the relationships within the Podocnemidae differ in that the Madagascan Erymnochelys is the sister taxon of the neotropical Podocnemis. Main conclusion
This result is in conflict with the hypothesis of pelomedusoid speciation being a result of the continental drift of South America and Africa/Madagascar, with the separation of those three continents resulting in three separate evolutionary groups. Based on an extensive fossil record, the Pelomedusoides are known to have been a wide-ranging group. This latest phylogenetic hypothesis, combined with that of Meylan (1996) for the Pelomedusoides, suggests that current pelomedusoid distributions and relationships could be the result of large-scale extinctions with extant taxa being relicts of this widespread group.